The present invention relates to a gear shift mechanism in a motor vehicle with a cab tiltable relative to the vehicle chassis and engine/transmission, comprising a lever receiving mounting arranged under the cab floor of the engine hood with a bearing for a gear shift lever, which extends into the cab through a through-hole in the floor or engine hood.
In trucks with front mounted tiltable cabs, in which the engine is usually mounted under the cab and is covered by a hood between the seats, the gear shift lever and associated linkages must be arranged so that they do not present an obstacle to the tilting movement. The arrangement should be such that the gear selector has distinct positions and it should only be minimally affected by the movements of the cab, which can, in todays modern trucks with comfortable spring mounted cabs, be relatively large in all directions relative to the chassis and engine/transmission. Furthermore, the gear selector mechanism should be sealed off effectively so that a low noise level can be maintained in the cab. Finally, the gear shift mechanism should be simple and reliable and permit tilting of the cab without any additional "releasing operations".
None of the solutions presented up to now fulfill all of these conditions. While it is true that gear selector mechanisms with the lever mounting fixed to the transmission usually have distinct positions and are only minimally effected by cab movements, they have either sealing problems (in unarticulated lever designs) because the hole in the engine hood or floor must be large or they require extra blocking mechanisms for the release means (for articulated lever designs) Swedish Patent No. 439,464.
Gear shift mechanisms with the shift lever bearing joined to the cab are simpler to seal in order to keep the noise level low, but in this case the shift lever must be able to somehow be released from the rest of the shift mechanism when the cab is tilted. These mechanisms are, however, affected by cab movements with indistinct gear speed positions as a result as well as problems with the gear selector being jolted out of gear when driving on uneven surfaces.
Gear shift mechanisms, in which the shift lever bearing is resiliently joined to the cab, are shown in German Patent No. 2,110,310 and U.S. Pat. No. 4,269,282, for example. In both of these mechanisms, the shift lever has a spherical end portion which is normally received in an opening in the gear transfer mechanism. This end portion is removed from this opening when the cab is tilted. The spring loaded mounting of the bearing in the cab permits limited shock absorbing movement of the cab without any problems, but large vertical cab movements or lateral movements present the risk that the spring loaded shift lever mounting housing will lose contact with its stationary support surface in the gear lever socket in the engine/transmission, resulting in play, misalignment and malfunctioning. Hard and rapid gear shifting can have the same result. Another disadvantage is that it is not possible to provide a connection free from play between the lever and the gear transfer mechanism. In order to permit disengagement and engagement, there must be a certain amount of play between the spherical end of the lever and the complementary socket in the gear transfer mechanism. This play increases with time due to wear and produces an even larger effect at the shift lever handle which produces indistinct gear selection.
The purpose of the present invention is to remove all of the above mentioned disadvantages and provide a shift mechanism of the type described by way of introduction, which is simple and reliable, has distinct gear positions, is simple to seal off to provide low noise level inside the cab, and which does not require any additional release steps prior to tilting the cab or any engaging steps after tilting the cab back to its operating position.